People with hepatitis C may have at least twice the risk of developing certain head and neck cancers as individuals who don't carry the virus, a U.S. study suggests.

While the hepatitis C virus (HCV) has long been linked to other cancers, including tumors of the liver and blood malignancies known as non-Hodgkin lymphoma, the findings are among the first to link it to cancers in the head and neck, researchers note in the Journal of the National Cancer Institute.

"With new medications available, HCV is treatable and curable with more than 90 percent success rate," said senior study author Dr. Harrys Torres of the University of Texas MD Anderson Cancer Center in Houston.

"Thus, the first step is to screen and treat infected patients, because antiviral treatment can prevent some cancers (e.g. liver cancer and non-Hodgkin lymphoma) from ever developing," Torres added by email. "It remains to be shown whether curing the infection reduces the risk of head and neck cancers," he cautioned.

To explore the cancer risk associated with HCV infection, Torres and colleagues analyzed data on almost 35,000 patients at MD Anderson Cancer Center tested for the virus from 2004 to 2014, a group that included 409 people with head and neck malignancies.

Overall, 20 percent of the people with what's known as oropharyngeal cancers - tumors in the middle and back of the throat, tonsils, soft palate and back of the tongue - had HCV. So did 14 percent of people with non-oropharyngeal cancers - tumors of the front and underside of the tongue, roof of the mouth, larynx, gums and lips.

Because smoking is a major risk factor for head and neck cancers, researchers also looked at data for a control group of 694 people with lung tumors and other smoking-related malignancies. They found 6.5 percent of this control group had HCV.

Compared with patients in the control group, the researchers found the risk for HCV-infected patients of developing head and neck cancers was increased: 2.4 times higher for oral cavity cancers, 2 times greater for oropharynx cancers and almost 5 times for larynx cancers.

One limitation of the study is the lack of a control group of cancer-free patients, the authors note. The findings also don't prove that HCV directly causes head and neck tumors.

Hepatitis C is usually spread when blood from an infected person enters the body of someone who isn't infected. These days, most people infected with the virus get it from sharing needles or equipment to inject drugs, but it can also be transmitted during sex, and until a test for it was developed in the early 1990s, people could acquire HCV through blood transfusions.

The Centers for Disease Control and Prevention recommends screening for people born during the "baby boom" generation from 1945 to 1965 and individuals with increased risk such those with AIDS or a history of drug use.

But a recent analysis of blood samples from nearly 5,000 emergency department patients seen at the Johns Hopkins Hospital in Baltimore found almost 14 percent tested positive for the virus - one third of whom didn't know they were infected.

If only people recommended for screening under the CDC guidelines got tested, 25 percent of the patients with undocumented hepatitis C wouldn't have been tested, that study found.

"The test is widely available and the consequences of not knowing your infection status can directly affect your health," said Dr. Thomas Quinn of Hopkins and the National Institute of Allergy and Infectious Diseases.

"Because hepatitis C virus can be cured, why not increase screening of the population and refer those that are positive to centers where they can be treated and thereby eliminate this associated risk for cancer," Quinn added by email.